Fix crash while searching in Settings

A crash occurrs when power button is pressed during search in Settings
due to IndexOutOfBoundsException in HeaderViewListAdapter.
When suggestions and results are cleared,
the layouts should be invisible to solve this problem.

Bug: 27913974
Test: manual - search "font" and press power button twice

Change-Id: Ia53d393e695dbb238fc4c82a3fe52ef4250d84c1